System and method for detecting an arc fault in a power line signal including a communication signal modulated on an AC power signal

ABSTRACT

An embodiment method of detecting an arc fault includes communicating a power line signal, including a communication signal modulated on an alternating current power signal, over a power line. The communication signal is communicated according to a power line network protocol. A power spectrum of the communication signal includes a first frequency band and a second frequency band different from the first frequency band. In accordance with the power line network protocol, a power of the communication signal in the first frequency band is attenuated in comparison to the power of the communication signal in the second frequency band. The method further includes performing arc fault detection on the spectral portions of the power line signal that are within the first frequency band.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/603,181, filed May 23, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/037,074, filed Sep. 25, 2013, now U.S. Pat. No.9,696,363, issued Jul. 4, 2017, which claims the benefit of U.S.Provisional Application No. 61/705,321, filed on Sep. 25, 2012, whichapplications are hereby incorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to electronic circuits, and moreparticularly to a system and method for an arc fault detector.

BACKGROUND

Digital and analog data communications over conventional utility andpremises electric power lines is an established method forpoint-to-point and point-to-multipoint communications between devices.In such communications, a communication signal carrying data issuperimposed on a 50 to 60 Hz alternating current (AC) power line usinghigher frequencies. A central computer may use such a power linecommunications system to control remote power applications, to monitorremote utility usage, or to support energy conservation. For example,the central computer may control the operation of heaters,air-conditioners, electric lighting and the like. The power linecommunications system may also be used to support high-speed broadbanddata to support Internet, multimedia and home entertainment systems,using a power line communication network such as IEEE 1901, IEEEP1901.2, HomePlug GP/AV/AV2/1.0, G.hn, G.hnem, and other similartechnologies.

The accuracy of arc fault detecting circuits on a power line thatincludes a power line communications system may be diminished as thepower line communications signal may be interpreted as an arc fault. Forexample, some arc detecting circuits analyze frequency noise content ona power line to detect arc faults, and the power line communicationssignal may have similar frequency noise content as that produced by anarc fault causing the arc detecting circuits to falsely identify thepower line communication signal as an arc fault.

SUMMARY

An embodiment is a method of operating an arc fault detection systemcoupled to a power line, the method including determining one or morearc fault detection windows in power line signals on the power line, thepower line signals comprising a communication signal and an alternatingcurrent (AC) power signal. The method further includes receiving thepower line signals from the power line during the one or more arc faultdetection windows, and performing arc fault detection processing on thereceived power line signals.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1A illustrates a time domain representation of a power linecommunication signal in accordance with an embodiment;

FIG. 1B illustrates a frequency domain representation of a power linecommunication in accordance with an embodiment;

FIG. 2 illustrates a power line communication system in accordance withan embodiment;

FIG. 3 illustrates a power line communication system in accordance withanother embodiment;

FIG. 4 illustrates a process flow diagram in operating a power linecommunication system in accordance with an embodiment;

FIG. 5 illustrates arcing spikes as related to the AC power line signal;and

FIG. 6 illustrates the frequency spectrum of arcing noise.

Corresponding numerals and symbols in different figures generally referto corresponding parts unless otherwise indicated. The figures are drawnto clearly illustrate the relevant aspects of embodiments of the presentinvention and are not necessarily drawn to scale. To more clearlyillustrate certain embodiments, a letter indicating variations of thesame structure, material, or process step may follow a figure number.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, that the present invention provides manyapplicable inventive concepts that may be embodied in a wide variety ofspecific contexts. The specific embodiments discussed are merelyillustrative of specific ways to make and use the invention, and do notlimit the scope of the invention.

The present disclosure will be described with respect to embodiments ina specific context, namely a system and method for an arc faultdetector. Embodiments of this invention may also be applied to othercircuits and systems, such as, but not limited to, communication systemssuch as power line communication systems.

Generally, embodiments of the present disclosure enable an arc faultdetector to determine quiet intervals and/or frequencies in a power linecommunication signal in such way that the arc fault detector canaccurately detect arc faults. By determining quiet intervals and/orfrequencies, the arc fault detector can more accurately identify an arcfault signature due to the decreased noise on the power line. Thedecreased noise on the power line may allow for simplified processingfor the arc fault detector and may reduce the incidence of a “falsepositive” detection of an arc fault.

For example, the power line modem may alert the arc fault detector toquiet intervals when the power line communication signals are of a lowvalue, intensity, periodicity, or the like, and the arc fault detectormay primarily perform arc fault detection during these quiet intervals.In some embodiments, the arc fault detector only performs arc faultdetection during these quiet intervals. In some other embodiments, thearc fault detector performs arc fault detection during quiet intervalsand during active intervals of the transmission of the power linecommunication signals, and the arc fault detector discounts the resultsof the arc fault detection during the active intervals.

In an embodiment, the power line modem schedules quiet intervals thatcorrespond to the intervals of the power line signal with the mostprominent arc fault signatures. These most prominent arc fault signatureintervals may be detected by the arc fault detector, which can alert thepower line modem of the intervals to allow the scheduling of the quietintervals. For example, the power line modem can suspend allcommunication for at least one cycle of the alternating current (AC)power signal so that the arc fault detector can “sweep” the noise duringthis suspended communication timeframe and the arc fault detector canfind the intervals in the AC power signal where the arc fault signaturesare most pronounced.

In an embodiment, the arc fault detector can request these suspensionsof communication (e.g., quiet intervals), and in other embodiments, thepower line modem may periodically schedule these quiet intervals andcommunicate them to the arc fault detector. In some embodiments, themost prominent arc fault signature intervals may be determinedbeforehand and the power line modem is configured to not transmit powerline communication signals during the predetermined intervals.

In an embodiment, the arc fault detector is capable of distinguishingbetween the signature of an arc fault and the signature of amulti-carrier signal, such as orthogonal frequency-division multiplexing(OFDM) signal. In some embodiments, the arc fault detector learns theproperties of the multi-carrier signal during intervals with the leastlikely arc fault signatures. For example, in some power networks, thearc fault noise is more prevalent in the zero crossing regions of the ACpower signal as shown in FIG. 5. In these power networks, the arccurrents spikes at the zero crossing regions causing high frequencynoise that may have a similar signature to a multi-carrier signal.

In some embodiments where the multi-carrier signal has been identified,the arc fault detector employs a multi-carrier signal cancellation suchthat the arc fault signature can be detected during the multi-carriersignal transmission. For example, the arc fault detector can know theenergy signature of the identified multi-carrier signal and thereforecan subtract the energy signature of the identified multi-carrier signalto allow the arc fault signature to be detected during a multi-carriersignal transmission.

In an embodiment, the arc fault detector takes into account the tones orfrequencies of known power line communication signals. The arc faultdetector may detect or learn these power line communication signals orthe power line communication signals may be supplied to the arc faultdetector by the power line modem. In some embodiments, the arc faultdetector ignores the tones or frequencies of the known power linecommunication signals. In other embodiments, the arc fault detectordiscounts the significance of the tones or frequencies of the knownpower line communication signals.

For example, in a HomePlug AV system, the power line communicationsignals are within substantially defined frequency bands in a range fromabout 2 MHz to about 90 MHz, whereas an arc fault signal can be spreadacross the frequency spectrum from about 0 Hz to hundreds of MHz asillustrated in FIG. 6. In some embodiments, the arc fault detectoranalyzes the low frequency component (e.g., from about 0 Hz to about 1MHz) of the power line signal to identify arc faults. In someembodiments, the arc fault detector analyzes the frequencies that arebetween the substantially defined frequency bands of the power linecommunication signal (e.g., the HomePlug AV signal).

In an embodiment, the arc fault detector and the power line modem arecoupled together outside of the power network and communicate by controlsignals. For example, the power line modem may notify the arc faultdetector of the quiet intervals and/or frequencies by way of the controlsignals. In addition, the arc fault detector may notify the power linemodem of the intervals in the power line signal with the most prominentarc fault signatures by way of the control signals so that the powerline modem may schedule quiet intervals during those intervals of thepower line signal. In some embodiments, the arc fault detector isintegrated into the power line modem. This allows for the protection ofthe power line modem and devices connected to the power line modem to beprotected from arc faults.

Embodiments of the present invention may be directed toward devices thatmay be configured to operate on a power line network, for example,consumer electronic devices, computing devices, appliances, and lightingsystems such as light-emitting diodes (LED) or compact fluorescent lamp(CFL) lighting. Devices, such as computing devices may use the powerline network to communicate with or to control other devices andappliances on the power line network and/or to access a local area orwide area network, such as the Internet.

FIG. 1A illustrates an embodiment of a power line communication signal,in the time domain, being transmitted and/or received by a power linecommunication system 100. The power line communication signal includesquiet intervals 20 and active intervals 22. The power line communicationsystem 100 may detect the active intervals 22 and the quiet intervals 22and may use the knowledge of these intervals to modify the operation ofpower line communication system 100 as discussed further below.

FIG. 1B illustrates an embodiment of a power line communication signalin the frequency domain. The power line communication signal includessubstantially defined frequency bands 30 (which may also be referred toas channels 30) and quiet bands 32 in which the power line communicationsignal is attenuated. As illustrated, the frequency bands 30 createlarge quiet bands 32 at frequencies below and above the frequency bands30. The power line communication system 100 may detect the active bands30 and the quiet bands 32 and may use the knowledge of these intervalsto modify the operation of power line communication system 100 asdiscussed further below. The quiet intervals 20 and the quiet bands 32may both be referred to as arc fault detection windows.

FIG. 2 illustrates a power line communication system 100 having a modem102, an arc fault detector 104, and an AC power line 106. The modem 102is coupled to the AC power line 106 via a communication interface 108and the arc fault detector 104 is coupled to the AC power line via thepower interface no. The modem 102 has a data I/O link 114 to transmitand receive digital data to and from an I/O device, such as a computingdevice, coupled to the modem 102. The modem 102 and the arc faultdetector 104 are coupled together by a control signal 112. In someembodiments, the modem 102 uses the control signal 112 to modify theoperation of the arc fault detector 104. In some embodiments, the arcfault detector 104 uses the control signal 112 to modify the operationof the modem 102.

In some embodiments, the modem 102 and the arc fault detector 104 of thepower line communication system 100 and other components described asperforming data or signal-processing operations constitute a softwaremodule, a hardware module, or a combined hardware/software module. Inaddition, each of the modules suitably contains a memory storage area,such as random access memory (RAM), for storage of data and instructionsfor performing processing operations in accordance with the presentinvention. Alternatively, instructions for performing processingoperations can be stored in hardware in one or more of the modules.

The AC power line 106 includes a power line communication network (seeFIGS. 1A and 1B as examples) such as IEEE 1901, IEEE P1901.2, HomePlugGP/AV/AV2/1.0, G.hn, G.hnem, or other similar technologies. In anembodiment where the AC power line 106 includes a power linecommunication network, such as an IEEE 1901 network, the modem 102 maybe a power line modem 102.

The arc fault detector 104 includes a memory (not shown) and an arcfault alarm 116. The arc fault alarm indicates an arc fault event hasbeen detected by the arc fault detector 104 and data corresponding todetected arc fault event may be stored in the memory of the arc faultdetector 104. In some embodiments, once an arc fault is detected, thearc fault detector 104 performs additional processing on the power linecommunication signal to try to obtain more information about the arcfault event such as the location of the event. In some embodiments, thememory of the arc fault detector 104 includes data representative ofidentifiable arc fault signatures, which can be used to determine thatan arc fault has occurred on the AC power line 106. The arc faultsignatures correspond to those signals that may be generated and/ortransmitted over a power line network when an arc fault event occurs onthe power line network. For example, the arc fault signature data mayinclude a unique radio frequency (RF) signature representative of thehigh frequency emission that occurs when the arc fault ignites and againwhen the arc fault extinguishes.

In some embodiments, the memory of the arc fault detector 104 includessignature data for the various power line network protocols such thatthe arc fault detector 104 can identify which power line networkprotocol (e.g., HomePlug AV, IEEE 1901, etc.) is in use. The arc faultdetector 104 may then use the identified protocol to determine quietintervals and/or quiet bands which may simplify the processing of thearc fault detection data as discussed below. The protocol data mayinclude preamble data or other characteristics of the various protocols.

In an embodiment, the arc fault detector 104 can identify amulti-carrier signal, such as an OFDM signal. The arc fault detector 104can learn the properties of the multi-carrier signal during intervalswith the least likely arc fault signatures. When the multi-carriersignal has been identified, the arc fault detector 104 can employs amulti-carrier signal cancellation such that the arc fault signature canbe detected more accurately while the multi-carrier signal is beingtransmitted.

In some embodiments, the modem 102 passes the protocol information tothe arc fault detector 104 by way of the control signal 112. When themodem 102 detects a quiet interval (see quiet intervals 20 in FIG. 1A)in the power line communication signal, the control signal 112 isactivated to alert the arc fault detector 104 of the quiet interval. Thequiet interval may simplify the monitoring and processing performed bythe arc fault detector 104 by permitting the arc fault detector 104 todetect an arc fault signature without the noise of the power linecommunication signal. The quiet interval may also increase the accuracyof the monitoring and processing performed by the arc fault detector104. In some embodiments, the arc fault detector 104 only performs arcfault detection during these quiet intervals. In some other embodiments,the arc fault detector 104 performs arc fault detection during quietintervals and during the active intervals (see active intervals 22 inFIG. 1A), and the arc fault detector 104 discounts the results of thearc fault detection during the active intervals of the power linecommunication signal.

In another embodiment, the modem 102 alerts the arc fault detector 104to quiet bands (see quiet bands 32 in FIG. 1B) in the power linecommunication signal by way of the control signal 112. Similar to thequiet intervals, the quiet bands may simplify the monitoring andprocessing performed by the arc fault detector 104 by permitting the arcfault detector 104 to detect an arc fault signature without the noise ofthe power line communication signal. In an embodiment, the arc faultdetector 104 only performs arc fault detection during these quiet bands.In another embodiment, the arc fault detector 104 performs arc faultdetection during quiet bands and during active bands (see active bands30 in FIG. 1B) and the arc fault detector 104 discounts the results ofthe arc fault detection during the active bands of the power linecommunication signal. In another embodiment, the arc fault detector 104analyzes a low frequency component of the power line communicationsignal for arc fault signature data, where the low frequency componentis in a range from about 0 Hz to about 1 MHz.

In an embodiment, the arc fault detector 104 is implemented as asoftware module. In another embodiment, the arc fault detector 104 isimplemented as a hardware module or a combined hardware/software module.By implementing the arc fault detector 104 as a hardware module or acombined hardware/software module, the amount of time required to detectan arc fault event may be decreased as hardware can respond faster thansoftware in many instances. For example, the arc detector may beimplemented in software running on a computational engine that receivesthe digitized signal from an analog-to-digital converter that samplesthe power line signals. The power line signals may undergo processingbefore the analog-to-digital converter, such as filtering and/oramplification.

FIG. 3 illustrates a power line communication system 120 with an arcfault detector 124 integrated within a modem 122. The details andoperation of the power line communication system 120 is similar to thepower line communication system 100 described above and the descriptionis not repeated herein, although the power line communication system 120and the power line communication system 100 need not be the same.

In another embodiment, the arc fault detector 124 or 104 may beintegrated with power line communication system that includes anintegrated switching power supply, as described in U.S. patentapplication Ser. No. 13/656,369 (now U.S. Pat. No. 9,130,657), entitled,“System and Method for a Power Line Modem,” which application isincorporated herein by reference in its entirety.

FIG. 4 illustrates a process flow 400 of a method in accordance with anembodiment. In step 402, one or more arc fault detection windows aredetermined in the power line signals on the power line. The arc faultdetection windows may be similar, for example, to the quiet intervals 20shown in FIG. 1A and/or the quiet bands 32 shown in FIG. 1B. Once thearc fault detection windows have been determined, in step 404, the powerline signals are received by the arc fault detector during the arc faultdetection windows. In step 406, the arc fault detection processing maybe performed on the received power line signals. Next, in step 408, thearc fault detector determines whether an arc fault was detected in thearc fault detection processing. If an arc fault was detected, a faultalarm is set in step 410. If an arc fault was not detected, the processrestarts at step 402 by determining more arc fault detection windows.

An embodiment is a method of operating an arc fault detection systemcoupled to a power line, the method including determining one or morearc fault detection windows in power line signals on the power line, thepower line signals comprising a communication signal and an alternatingcurrent (AC) power signal. The method further includes receiving thepower line signals from the power line during the one or more arc faultdetection windows, and performing arc fault detection processing on thereceived power line signals.

Another embodiment is an arc fault detection system configured to becoupled to a power line, the arc fault detection system including an arcfault detector configured to detect an arc fault on the power line, anda power line modem configured to transmit and receive data on the powerline. The power line modem includes a first node configured to becoupled to the arc fault detector, the first node being configured tosignal the arc fault detector to modify detection behavior of the arcfault detector.

A further embodiment is a system including a power line modem configuredto be coupled to a power line, the power line modem being configured todetect a quiet interval in a transmission on the power line and indicatevia a first control signal that a quiet interval is being detected. Thesystem further includes an arc fault detector coupled to the firstcontrol signal and configured to be coupled to the power line, the arcfault detector modifying its detection behavior such that arc faultdetection is more accurate during the quiet interval.

Advantages of embodiments include the ability to achieve accurate arcfault detection on power lines that include a power line communicationsystem. Because, the power line communication signal can have asignature that may be similar to the signature of an arc fault,analyzing the power line communication signal during a quiet interval,the accuracy and speed of the arc fault detection may be increased, asthe processing required to detect the arc fault may be simpler thanprocessing the arc fault detection during an active interval of thepower line communication signal. Further advantages of some embodimentsinclude the integration of an arc detector with a power line modem suchthat the power line modem and devices connected to it are protected fromarc faults.

The following U.S. patent application Publications and U.S. patents areincorporated herein by reference in their entirety: U.S. Pat. No.6,917,888, entitled, “Method and system for power line network faultdetection and quality monitoring;” U.S. Pat. No. 7,106,177, entitled,“Method and system for modifying modulation of power line communicationssignals for maximizing data throughput rate;” U.S. Pat. No. 7,193,506,entitled, “Method and system for maximizing data throughput rate in apower line communications system by modifying payload symbol length;”U.S. Pat. No. 7,369,579, entitled, “Method and system for timingcontrolled signal transmission in a point to multipoint power linecommunications system;” U.S. Pat. No. 7,683,777, entitled, “Method andsystem for audio distribution in installations where the use of existingwiring is preferred;” U.S. Pat. No. 7,804,673, entitled, “Intelligent,self-aware powerline conditioning and communication node;” and U.S. Pat.No. 8,115,605, entitled, “Power line communications device in whichphysical communications protocol layer operation is dynamicallyselectable.” Systems and methods described in the above mentioned U.S.patents can be applied to embodiments described herein.

It will also be readily understood by those skilled in the art thatmaterials and methods may be varied while remaining within the scope ofthe present invention. It is also appreciated that the present inventionprovides many applicable inventive concepts other than the specificcontexts used to illustrate embodiments. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method of communicating over a power line, themethod comprising: communicating a power line signal over the powerline, wherein the power line signal comprises a communication signalmodulated on an alternating current (AC) power signal, wherein thecommunication signal is communicated according to a power line networkprotocol, wherein a power spectrum of the power line signal comprises atleast one first frequency band and at least one second frequency bandthat is different from the at least one first frequency band, wherein,in accordance with the power line network protocol, a power of the powerline signal in the at least one first frequency band is attenuated incomparison to the power of the power line signal in the at least onesecond frequency band; and performing arc fault detection on spectralportions of the power line signal that are within the at least one firstfrequency band.
 2. The method of claim 1, wherein the at least one firstfrequency band is outside a band from 2 MHz to about 90 MHz.
 3. Themethod of claim 2, wherein the at least one first frequency bandcomprises frequencies less than 1 MHz.
 4. The method of claim 2, whereinthe at least one first frequency band comprises frequencies greater than90 MHz.
 5. The method of claim 1, wherein the at least one secondfrequency band comprises non-overlapping bands of frequency, and whereinthe at least one first frequency band is between the non-overlappingbands of frequency.
 6. The method of claim 1, wherein the at least onefirst frequency band comprises frequencies greater than 35 MHz.
 7. Themethod of claim 1, further comprising receiving information indicativeof the power line network protocol.
 8. The method of claim 7, furthercomprising detecting or learning spectral portions of power line signalthat are within the at least one first frequency band based on theinformation.
 9. The method of claim 1, wherein the power line signal iscommunicated through a power line modem and wherein the arc faultdetection is performed by an arc fault detector.
 10. The method of claim1, wherein the communication signal comprises a multi-carrier signal.11. A method of operating an arc fault detection system coupled to apower line, the method comprising: communicating a power line signalover a power line, wherein the power line signal comprises acommunication signal modulated on an alternating current (AC) powersignal, wherein the communication signal is communicated according to apower line network protocol, wherein a power spectrum of the power linesignal comprises a first frequency band and a second frequency band thatis different from first frequency band, wherein, in accordance with thepower line network protocol, a power of the power line signal in thefirst frequency band is attenuated in comparison to the power of thepower line in the second frequency band; designating spectral portionsof the power line signal that are within the first frequency band as anarc fault detection frequency window; and performing arc fault detectionon spectral portions of the power line signal that are within the arcfault detection frequency window, wherein no arc fault detection isperformed on spectral portions of the power line signal that are outsideof the arc fault detection frequency window.
 12. The method of claim 11,wherein the first frequency band comprises frequencies less than 1 MHzor frequencies greater than 90 MHz.
 13. The method of claim 11, whereinthe second frequency band comprises non-overlapping bands of frequency,and wherein the first frequency band is between the non-overlappingbands of frequency.
 14. The method of claim 11, wherein thecommunication signal comprises a multi-carrier signal.
 15. A systemcomprising: a power line modem configured to be coupled to a power lineand to modulate and demodulate a communication signal on an alternatingcurrent (AC) power signal of the power line, wherein the AC power signaland the communication signal form a power line signal on the power line,wherein the power line signal is communicated according to a power linenetwork protocol, wherein a power spectrum of the power line signalcomprises a first frequency band and a second frequency band that isdifferent from the first frequency band, wherein, in accordance with thepower line network protocol, a power of the power line signal in thefirst frequency band is attenuated in comparison to the power of thepower line signal in the second frequency band; and an arc faultdetector coupled to the power line modem and configured to: identifyspectral portions of power line signal that are within the firstfrequency band; and perform arc fault detection on the spectral portionsof the power line signal that are within the first frequency band. 16.The system of claim 15, wherein the power line modem is coupled to thearc fault detector and configured to control the arc fault detection bythe arc fault detector.
 17. The system of claim 16, wherein the powerline modem is configured to control the arc fault detection of the arcfault detector by identifying the power line network protocol.
 18. Thesystem of claim 15, wherein the arc fault detector is integrated withthe power line modem.
 19. The system of claim 15, wherein the arc faultdetector is configured to signal the power line modem to modifytransmission behavior of the communication signal on the power line inresponse to a detection of an arc fault in the power line signal. 20.The system of claim 19, wherein the arc fault detector is configured tosignal the power line modem to request, from the power line modem,information indicative of the first frequency band.
 21. The system ofclaim 20, wherein the arc fault detector is configured to identifyspectral portions of power line signal that are within the firstfrequency band based on the information receved from the power linemodem.